Re: [RFC] Unify KVM kernel-space and user-space code into a single project

On 03/22/2010 02:17 AM, Ingo Molnar wrote:> * Anthony Liguori<anthony@codemonkey.ws> wrote:> >> On 03/19/2010 03:53 AM, Ingo Molnar wrote:>> >>> * Avi Kivity<avi@redhat.com> wrote:>>> >>>>> There were two negative reactions immediately, both showed a fundamental>>>>> server versus desktop bias:>>>>>>>>>> - you did not accept that the most important usecase is when there is a>>>>> single guest running.>>>>> >>>> Well, it isn't.>>>> >>> Erm, my usability points are _doubly_ true when there are multiple guests ...>>>>>> The inconvenience of having to type:>>>>>> perf kvm --host --guest --guestkallsyms=/home/ymzhang/guest/kallsyms \>>> --guestmodules=/home/ymzhang/guest/modules top>>>>>> is very obvious even with a single guest. Now multiply that by more guests ...>>> >> If you want to improve this, you need to do the following:>>>> 1) Add a userspace daemon that uses vmchannel that runs in the guest and can>> fetch kallsyms and arbitrary modules. If that daemon lives in>> tools/perf, that's fine.>> > Adding any new daemon to an existing guest is a deployment and usability> nightmare.> Absolutely. In most cases it is not desirable, and you'll find that in a lot of cases it is not even possible - for non-technical reasons.One of the main benefits of virtualization is the ability to manage and see things from the outside.> The basic rule of good instrumentation is to be transparent. The moment we> have to modify the user-space of a guest just to monitor it, the purpose of> transparent instrumentation is defeated.> Not to mention Heisenbugs and interference.

CheersAntoine

> That was one of the fundamental usability mistakes of Oprofile.>> There is no 'perf' daemon - all the perf functionality is _built in_, and for> very good reasons. It is one of the main reasons for perf's success as well.>> Now Qemu is trying to repeat that stupid mistake ...>> So please either suggest a different transparent solution that is technically> better than the one i suggested, or you should concede the point really.>> Please try think with the heads of our users and developers and dont suggest> some weird ivory-tower design that is totally impractical ...>> And no, you have to code none of this, we'll do all the coding. The only thing> we are asking is for you to not stand in the way of good usability ...>> Thanks,>> Ingo> --> To unsubscribe from this list: send the line "unsubscribe kvm" in> the body of a message to majordomo@vger.kernel.org> More majordomo info at http://vger.kernel.org/majordomo-info.html>